Botulinum neurotoxin is an ongoing public health problem and is considered to be a potentially serious biological warfare agent. Recent worldwide events including the discovery of stockpiles of materials for manufacture of the toxin by extremist groups in Japan and Iraq have shown that the danger exists for biological terrorism. Intoxication from the toxin by consumption in food or water or from inhalation can lead to prolonged paralysis, incapacitation, and need for intensive supportive care. Depending on the route of administration, death can result from exposure to less than a microgram of toxin. There are no effective therapies once symptoms of botulism appear other than supportive treatments such as intubation and ventilation.
Within the last five years a number of potential therapies have been identified (e.g. aminoquinolines, metalloprotease inhibitors, aminopyridines. Adler, et al., 1996), and zinc chelators such as TPEN (Adler, et al., 1997). None of these are likely to work in vivo due to difficulty in penetration into the neuronal cytosol and high systemic toxicity. Although better metalloprotease inhibitors have recently been developed at the University of Wisconsin-Madison (Dr. Daniel Rich), these are likely to be limited by the same problems of membrane penetration and toxicity as the first generation of drugs. Anything that crosses lipid membranes easily will also be likely to cross the blood-brain barrier and have CNS toxicity. Any potential therapeutic compound that cannot be internalized into the nerve terminal cytosol will not be capable of antagonizing the active component of botulinum neurotoxin.
In one embodiment, the present invention is a method of targeting therapeutic molecules to motor neurons. This method preferably comprises the step of (a) synthesizing a prodrug comprising a therapeutic molecule covalently bound to a polymeric delivery vehicle and (b) conjugating the prodrug to a botulinum neurotoxin heavy chain. In a preferred method of the present invention, the prodrug comprises at least two copies of the therapeutic molecule.
In another preferred method of the present invention, the botulinum neurotoxin heavy chain is type A botulinum neurotoxin and the therapeutic molecule is a metalloprotease inhibitor.
It is an object of the present invention to target therapeutic molecules to motor neurons.
Other objects, features and advantages of the present invention will become apparent after one has reviewed the specification, claims and drawings.